Rotary press folding machines are generally well known in the art of printing. Such folding machines are commonly employed to impart one or more folds on printed materials such as catalogs, brochures, and especially newspapers.
Newspapers are most commonly folded in one of two basic formats. The first format, referred to as "broadsheet", has two folds in each section. The first fold (known as the side fold) runs vertically and extends perpendicular to the masthead, while the second fold (known as the end fold) runs horizontally and folds the already folded section in half. In contrast, the second format, referred to as "tabloid", has only the single side fold. The New York Times, the Washington Post, and the Chicago Tribune are representative examples of "broadsheet" formats, while the New York Daily News, the National Enquirer, and the Chicago Sun-Times are representative examples of "tabloid" formats. Typically, the same machinery, commonly called a second fold roller, is used to form the side fold of a thicker "tabloid" newspaper as well as the second fold or end fold of a "broadsheet" paper.
Second fold rollers are well known in the art. On a conventional second fold roller, a printed newspaper having a continuous web of superimposed printed sheets or pages is cut into sections and routed to a folding drum having a folding blade. The folding blade forces each cut section into a gap between a pair of counter-rotating folding rollers, which pinch the section along the desired fold line as the section is forced through the small gap between the rollers. Ideally, the gap between the rollers is slightly smaller than the thickness of the paper in order to ensure that the fold is formed properly. Typically, the gap is set at a minimum size, and a system of control springs that are set at a desired force level cause the rollers to be biased towards each other, yet permit the folding rollers to separate slightly as the paper passes through the gap. After exiting the rollers the folded paper drops onto an exit conveyor in a manner well known in the art.
The folding process occurs at very high speeds, and thus the size of the gap between the folding rollers, as well as the force exerted by the control springs which urge the folding rollers together, must be precisely controlled in order to achieve fast, consistent folds without jamming. A jam typically occurs when a paper gets stuck in the gap. When this happens, two, three, or more papers become stuck in the gap in rapid succession. The folding rollers must then be separated before the jammed papers can be removed. Thereafter, the folding rollers must be returned to their desired position with the correct gap size and the proper amount of control spring force.
One serious disadvantage of prior art folding machines is that, in the event of a jam, it is very time consuming to separate the rollers, remove the jammed papers, and return the rollers to their desired position with the proper amount of control spring force. Typically, the control spring or springs must be removed or otherwise disengaged before the rollers can be separated, and unfortunately these control springs are relatively inaccessible. After the jam has been cleared, correct gap size between the folding rollers must be restored and the control spring or springs must be re-engaged and re-adjusted to the desired pressure. The entire process is very labor intensive, time consuming, and increases the down time of the printing press which consequently greatly reduces productivity.
Another problem faced by prior art folding machines is that, when the thickness of the papers being folded changes, the machine must be stopped and the gap size between the folding rollers must be adjusted to suit the different paper thickness. This gap adjustment in turn changes the tension of the control springs, and thus it is necessary to re-adjust the relatively inaccessible control springs to the desired force level. Like the jam removal process outlined above, the gap adjustment process is similarly labor intensive, time consuming, and subject to operator error. Accordingly, there exists a need for a gap adjustment device on a second fold roller that is easier to adjust and calibrate and that enables the operator to quickly and easily remove jammed papers and return the rollers to their operative positions with the proper control spring force.